1. Field of the Invention
The present invention relates to a method for extracting an iris region from an image of an eye of an animal or a human and more particularly to an individual identification device based on an iris code.
2. Description of the Related Art
Technologies for individual identification using an iris of an eye are conventionally used. The individual identification technology of this kind is disclosed, for example, in U.S. Pat. No. 5,291,560 or Japanese PCT Publication No. 8-504979. For individual identification, the conventional technology takes the following procedures:
1. A picture of an eye is taken by a camera or the like and a circle having its center in a pupil is applied to a border between the pupil and an iris and a border between the iris and a sclera. The circle is used as an internal border and an external border of the iris respectively.
2. A region between the borders of the iris is split into some ring-like bands and information about configuration of a pattern of each ring-like band is extracted by convolution technology using a 2-D Gabor filter and the extracted region is encoded by a value 0 (zero) or 1 in accordance with its amplitude.
3. The Hamming distance between an iris code registered in advance and an iris code produced using an inputted image is computed to authenticate individual identification.
In the conventional method, however, since the iris region is extracted on the precondition that the pupil is circular, in the case of an animal the pupil of which is elliptic, high accurate extraction of the iris region has been impossible.
FIG. 2 is an explanatory view of an eye of a human. FIG. 3 is an explanatory view of an eye of an animal. FIG. 3(a) shows an eye of a horse, (b) shows an eye of a dog and (c) shows an eye of a cat. As depicted in FIG. 3(a), contours of the pupil and the iris of the horse are not circular. Moreover, because there is a substance called a granula iridia on the contour line on the upper portion of the pupil, it is impossible to accurately extract the contour line of the pupil. Additionally, in the eyes of the animals as shown in FIG. 3(a) to (c), the border between the iris and the sclera hides behind an eyelid in many cases, so it is difficult to extract this contour line.
On the other hand, a method for producing iris codes by using the conventional method except the technique of approximation of the contour line in which an ellipse is used instead of the circle seemed possible; however, it has been proved that this method can not be applied to some sizes of the pupil where exact extraction of the contour line is impossible.
FIG. 4 is an explanatory view of states of dilatation and narrowing of the pupil. When an ellipse is applied to the pupil being narrowed as shown in FIG. 4(a), errors in the application occur in the vicinity of both ends of a long axis in particular, causing unstable setting of a system of coordinates and low accuracy in checking.
Moreover, the direction of movement of the iris pattern at the lower portion of the iris and at its both ends in response to changes of the pupil caused by brightness is as shown in FIG. 4 (the size of an arrow shows the amount of the movement). Therefore, when the iris pattern is expressed by a system of polar coordinates having its center in the pupil, the position of the iris pattern differs depending on the state of dilatation or narrowing of the pupil, causing disconformity of iris codes for identification.
As described above, the conventional individual identification presents a problem in that this method can not be employed for sufficiently accurate individual identification of animals such as a horse or cattle.
In view of the above, it is an object of the present invention to provide a method for accurately extracting an iris region even when a position of a pupil is changed.
According to a first aspect of the present invention, there is provided a method for extracting an iris region from an eye image obtained by taking a picture of an individual comprising steps of:
applying a circular arc to part of a border line between a pupil region and the iris region contained in the eye image; and
setting a contour line outside the iris region on another circular arc having the same center as the above circular arc has.
In the foregoing, a preferable mode is one wherein a radius of the other circular arc being associated with a central angle of the circular arc applied for every individual is estimated.
Also, a preferable mode is one wherein the iris region is split in two directions, one being along the circular arc and the other being orthogonal to the circular arc and predetermined image processing is performed on each of split bands for encoding and obtaining two iris codes.
According to a second aspect of the present invention, there is provided a method for extracting an iris region from an eye image obtained by taking a picture of an individual comprising steps of:
applying an ellipse to a pupil region contained in the eye image; and
estimating a radius of a border line outside the iris region based on a ratio of a long axis to a short axis of the ellipse.
According to a third aspect of the present invention, there is provided an individual identification device comprising:
a pupil contour extracting means to extract a contour of a pupil region from an eye image obtained by taking a picture of an individual;
a pupil circle/iris circle setting means to apply a circular arc to part of a contour of a pupil region extracted by the pupil contour extracting means and to obtain a border line outside the iris region based on a central angle of said circular arc;
an iris code producing means to produce an iris code of the iris region set by the pupil circle/iris circle setting means; and
an iris code comparing means to compare the iris code produced by the iris code producing means with an iris code registered in advance and to use the result for individual identification of the eye image.
According to a fourth aspect of the present invention, there is provided an individual identification device comprising:
a pupil contour extracting means to extract a contour of a pupil region from an eye image obtained by taking a picture of an individual;
a pupil circle/iris circle setting means to apply a circular arc to part of a contour of a pupil region extracted by the pupil contour extracting means and to obtain a border line outside the iris region based on a central angle of the circular arc;
a first iris code producing means to produce the iris code of the iris region set by the pupil circle/iris circle setting means along the direction of a circumference of the iris region;
a second iris code producing means to produce the iris code of the iris region set by the pupil circle/iris circle setting means along the direction being orthogonal to the circumference; and
an iris code comparing means to compare two iris codes produced by the first and second iris code producing means with an iris code registered in advance and to use the result for individual identification of the eye image.
Also, a preferable mode is one wherein the iris code comparing means outputs two degrees of dissimilarities between the produced iris code and the registered iris code, and there is provided a composite judging section to obtain a composite degree of dissimilarities from the two degrees of dissimilarities and to judge based on the composite degree of dissimilarities whether the produced iris-code conforms to the registered iris code.